Trays made from injection moulding are commonplace in the Integrated Circuit (IC) and semiconductor industries for transporting sensitive components. These trays are covered by various industry standards, such as JEDEC, EIAJ, EIA and others.
The trays are manufactured using injection moulding in various polymers, for example, PPO, PPE, PP, PC, PSU, PES, PAS and ABS. The polymers are usually filled to provide strength and conductivity. Various materials are often used such as talc, carbon fibre, carbon powder, metal fibre and the other usual polymer fillers.
The most common use of the trays is in transporting and protecting the components through the stages of assembly, test and distribution. Each tray contains pockets, each pocket designed to accept a component. The component sits securely in the pocket, with as little free movement as possible. Within each tray, the pockets are arranged in a rectangular matrix and with a regular pitch, according to the standard, in order to facilitate robot pick and place operations. A tray will typically be able to hold between 1 and 2,500 components, depending on the size of the component and the pitch of the rectangular matrix. New trays are often designed for every requirement, e.g. component size and type.
Each tray has features defining pockets on both the top and bottom surfaces. In this way a single tray can securely hold a component in X and Y planes, to present the component for inspection or processing, in a “live bug” or “dead bug” orientation, depending on which side of the tray is used to hold the component.
Each tray is designed so as to be static dissipative or conductive. They conduct electrically to a certain specification and will dissipate static charges, thereby protecting the components stored within the pockets from the adverse effects of any static charges.
So far, the component trays have been discussed individually. When used in combination, two similar trays can provide enhanced transport protection by creating a 3D enclosure surrounding the component. The pocket on the bottom side of the first tray cooperates with the pocket on the facing top side of the second tray, each pocket thus being one half of the whole pocket or 3D enclosure surrounding the component. To avoid ambiguity, the whole pocket defined by the cooperative pockets of the top and bottom surfaces of adjacent trays will hereafter be referred to as the 3D enclosure. Two trays, in a stacked pair, thus provide transport protection in both horizontal and vertical planes.
When designing these injection moulded trays, the size of the pocket must conform as closely as possible to the size of the component it is designed to carry. In this way, the free movement of the component is reduced in both horizontal and vertical directions, preventing damage to the component. However, in order to accommodate manufacturing tolerances both of the components and the trays, the pockets are designed to be slightly larger than the components they are designed to carry. There should be free play between the component and the pocket inner walls. The oversized pockets are sized in such a way that the component does not fall from any seating ledges that may be present in the pocket due to too wide a gap and is not prevented from fully going down into the pocket. In general, all pocket designs incorporate a taper or draft angle on the walls (whether by intention or by way of the injection molding process). The molding process necessitates a usual draft taper of 5 degrees, and anything larger than that is intentional design. The wall taper ensures that the component automatically self-aligns or self-centers, and/or falls squarely into the central portion of the pocket and onto the seating ledges, where provided.
Typically, one tray is designed to fit one specific type or size of component. Some trays however, are designed to protect multiple types and sizes of component. As the tray system through the 3D enclosures provides 3-dimensional protection, to protect multiple components compromises must be made. These include an inefficient use of available space, too much free movement of the component within the pockets or 3D enclosures thus affording less protection to the component, or a loss of rigidity of the tray, again decreasing the afforded protection.
In some cases, the size of the component will vary during different stages of production as they progress down the assembly line process, from the addition or assembly of sub-components and materials that add to or subtract from the initial component. The tray must be able to adequately protect the largest size of component during production, however must also provide adequate protection during smaller phases. Manufacturing multiple trays for each stage is not only cost intensive but also space consuming and inconvenient in terms of having to use separate trays for each stage.
Various solutions have been proposed to counteract this issue, each with inherent downfalls. One method, as described in U.S. Pat. No. 6,612,442, is to manufacture the trays using a thermoforming process, rather than injection moulding. The trays provide storage and cost savings over injection moulded trays, however suffer from a lack of rigidity inherent in thermoformed products.
An injection moulded peripheral frame can be used to provide a modicum of rigidity, as is also described in U.S. Pat. No. 5,547,082. These solutions suffer from a tendency for the pockets to lose their shape. By using a peripheral, featureless frame, the thermoformed sheet is not held securely and the sheet can ‘sag’, moving away from the sheet's restraining points. Protection for the components is thus compromised during transport and use, especially when the tray is used singly and not as a stacked pair.
Other solutions, such as US 2005/0072714 and US 2005/0072715, use a featureless injection moulded base tray as mentioned above, but use an injection moulded insert to provide the various pocket sizes required to house the component. Although these inserts provide a removable method of altering the pocket size for the intended purpose, they are expensive to produce, slow to design and manufacture and require a large amount of storage space.
Other methods of transporting components can be used such as tubes and carrier tape and reel, but these do not provide the protection and easy accessibility of the conventional tray system.